@Trainmstr I'm impressed with your skills using SCARM and how you've fit all this track together. I can tell you put a lot of time and effort into it.
I opened your most recent SCARM file. At the back of the walk-in open area in the middle of the layout (in the picture top right) where the tracks run side by side around the inside corner (O-32, O-42, O-42), they are so close together that passing trains and cars on adjacent tracks will likely hit or scrape each other, especially longer locomotives and cars and ones with overhanging ends.
You've mentioned wanting buildings. When planning my layout, I got all my buildings and larger trackside accessories out of their boxes and wrote down their dimensions, noting the length as the side that would be facing the track. In SCARM, I created simple rectangles and/or circles (using Figures) to represent placements for the buildings I wanted to include on my layout.
Deciding which industries you want to include will help guide your layout plan. Like most of us in this hobby, you may not be able to include everything you want. Only you can decide what to include and what might be swapped out later for something else.
At this point, my suggestion is if you want more than a purely loop running and switching layout, as in, if you also want to have industries, consider scaling back the yard and/or the turntable, placing the buildings and industries, then fill in around those with track.
A tip for working with a complex layout such as yours in SCARM is to separate sections of track into Layers. Doing this allows the different layers to be active, visible only, or hidden. Some examples: main level outer loop, yards, TT & whisker tracks, upper level, alternative ideas that you may not want to delete, but just hide temporarily.
